In a high output semiconductor device having a lot of units each of which constitutes a field effect transistor having a source electrode, a gate electrode, and a drain electrode and which are alternately connected in parallel with each other in a finger-shape, a device is necessary to ease a phase difference to a high frequency signal between gate electrodes and to prevent an uneven operation. Further, in a high frequency operation, an oscillation occurs when a gain of at least one is obtained in a frequency in which an electric delay time between respective units is set to a half cycle.
As a solving means, a conventional semiconductor device employs a method of using a unit cell, in which a plurality of units as field effect transistors each having a source electrode, a gate electrode, and a drain electrode are connected to each other in a finger-shape as a basic structure, disposing resistive elements between gate bus wirings between adjacent unit cells as to gate bus wirings by which a plurality of the gate electrodes constituting the units are bundled, and electrically connecting adjacent unit cells (JP-A H7-111271 (KOKAI)). With this arrangement, an oscillation can be suppressed by absorbing an uneven high frequency operation between the unit cells by the resistive elements.
Since the gate bus wirings positioned in the vicinity of the electric field effect transistors are affected by the heat generated when a semiconductor device is operated, the resistive elements connected to the gate bus wirings are also affected by the heat when the semiconductor device is operated. Since the resistance value of a conventionally used resistive element using a metal thin film is varied by an operation temperature, the resistive element arises a problem in a stable operation when it is used for a high output device that accompany high heat generation.
In particular, in a high frequency/high output semiconductor device using gallium nitride (GaN) which is expected as a semiconductor material of a next generation, a high frequency/high output operation is required in a high temperature environment due to the excellent physical property of the material. From what has been described above, a more serious problem is caused by heat. In addition to the above problem, in the high frequency/high output semiconductor device which is required to exhibit a high output in a limited chip size, since a space between the bus wirings of a unit cell is limited, the size of a resistive element which can be installed in the space is limited.